Another International Security piece with some careful empirical work and important conclusions: Testing the Surge Why Did Violence Decline in Iraq in 2007? by Stephen Biddle, Jeffrey A. Friedman, and Jacob N. Shapiro.
By August 2006, casualties were running at 1,500 a month for Iraqi civilians and 100 a month for the US military; from June 2008 to June 2011, these monthly averages fell to 200 and 11 respectively. (p.7) What explains the fall?
The authors dismiss the ethnic cleansing hypothesis – that the “unmixing” of Sunni-Shia neighborhoods was key – by pointing out that much of the violence occurred in Sunni-dominated Anbar Province, and that the urban violence didn’t stop when Sunnis were driven out. (p.15)
That leaves two explanations: first, the ”surge” of US forces in 2007 and, second, the 2006-7 Sunni tribal uprising against Al Qaida in Iraq (AQI), known as the “Anbar Awakening” or, sometimes, “Sons of Iraq” (SOI). The paper argues that both were necessary but insufficient, and worked in concert with each other. Previous Sunni re-alignments had failed because there weren’t enough US troops to protect the defectors, but the new troops would have had a weaker effect were it not for the Awakening:
The results suggest that SOIs played a crucial role in reducing Iraq’s violence in 2007. As table 2 shows, 24 of 38 AOs [Areas of Operations] where SOIs stood up (63 percent) show violence trending downward more sharply after SOI standup than before. The difference, moreover, is large: across all 38 AOs, the average rate of reduction before SOI standup was 2.5 percentage points per month; the rate after standup was 5.8 percentage points per month, or roughly two and a half times greater. (p.28, emphasis added)
In other words, if you had the surge but no Awakening,
then violence might have declined so slowly that Iraq— especially Iraq’s key terrain—would have been far from stabilized when the surge ended. The first surge brigade deployed in February 2007; the last surge brigade withdrew in July 2008. If violence had declined only at a rate of two percentage points per month throughout this period (as seen, on average, prior to SOI standup), then violence when the surge ended would have been no lower than in mid-2006, and this after another ten months of intense combat not seen in the historical case. Without SOIs, the data suggest that it could have taken more than three years of grinding warfare with surge-scale troop levels to bring the violence down to the levels achieved in a few months with the SOIs; without the Awakening, violence would have remained very high for a very long time—and certainly long after the surge brigades had gone home. (p.33, emphasis added)
In other words, troop surges only work when other factors are present. The authors have a cautionary note for Afghanistan:
COIN optimists saw Iraq as grounds for supporting a comparable surge in Afghanistan. The 2008–09 reinforcements there may or may not have been wise, but if they were advisable it was not because of Iraq: Afghanistan has not produced a movement analogous to the Awakening, and without this one should not expect 2007-like results. If the Afghan surge works, it will be a longer, tougher slog … In Afghanistan, by contrast [to the SOI], programs such as the Afghan Public Protection Police (APPP) and the Afghan Local Police (ALP) do not represent organized cells of former insurgents changing sides—they must therefore face an undiluted threat with only limited training and equipment. (p.37, emphasis added)
In other words, “U.S. reinforcements and doctrine played an essential role in 2007—but so did local conditions that will not necessarily recur elsewhere. U.S. policy thus deserves important but partial credit for the reduction of violence in Iraq, and similar results cannot necessarily be expected from similar methods in the future”. (p.11) It’s obvious that this is a politically-charged finding:
Finally, this suggests a causal mechanism for troop surges that is not about the ‘hearts and minds’ emphasized in most COIN thinking:
There is no evidence, however, that the 2007 turnaround occurred because some group of nonaligned civilians changed their minds and decided to support Nouri al-Maliki’s government. Especially after the sectarian escalation of 2006, Iraq was a polarized society of highly mobilized sectarian identity groups that were unlikely to support sectarian rivals in response to an offer of better services. In fact, when the Sunni insurgency changed sides in the Awakening, it did so not by allying with the Shiite government of Iraq (GoI), as SOI contracts were negotiated with U.S. soldiers. And what realigning Sunnis needed from these Americans was not large-scale economic development or assistance in public administration, but combat power to protect them from counterattack by their erstwhile comrades (and U.S. protection from the GoI: many SOI leaders wanted U.S. commanders to keep the ISF [Iraqi Security Forces] out of the SOIs’ operating areas, and the Americans often complied) … Iraq’s causal dynamics in 2007, however, appear to have had more to do with combat than with winning hearts and minds via service delivery. (p.38, emphasis added)